what's that small peak prior to G1?

I am just wondering if anyone of you have ever seen such a cell cycle pattern like this before for a mammalian cell line. This is untreated cells so I only expect to see a G1 and G2/M peak but I got an extra peak that I've never seen before in another batch of the same cell line or different cell line. Any opinion is hugely appreciated.

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The peak that is calculated as 52% is the G1 peak (at channel 200). G2/M is then around channel 400. The peak below the G1 is generally referred to as the Sub G1 peak and is indicative of cells that have undergone some DNA degradation due to apoptosis. One way to confirm this would be to display the DNA content on the x-axis and then forward scatter on the y-axis. The Sub G1 cells should be both low in the DNA content axis and low on the FSC channel. For more information on Sub G1, you can see: Kajstura M, Halicka HD, Pryjma J, Darzynkiewicz Z. Discontinuous fragmentation of nuclear DNA during apoptosis revealed by discrete "sub-G1" peaks on DNA content histograms. Cytometry A 2007; 71A:125-131

thank you very much for the response. This indeed confirmed that the small peak below g1 is apoptotic cells. I wasn't sure because I was using untreated cell lines and was expecting no subg1 peak at all. But the fact that it is present suggests that the cells may be basally apoptotic. I compared this with the same cell line grown in another lab and there was no subg1 peak with theirs.